1. Field of the Invention
The present invention relates to a hierarchical control apparatus of a hierarchical storage system in which a disk array apparatus and a library apparatus are hierarchically confirmed, and a method for maintaining and managing duplexed media.
2. Description of the Related Art
FIG. 5 shows a structure of a conventional hierarchical storage system. In FIG. 5, numeral 50 denotes a hierarchical control apparatus, numeral 51 denotes a disk array apparatus having a plurality of hard disks 510, numerals 52-0 and 52-1 denote duplexed library apparatus, numerals 520-1 to 520-n and 521-1 to 521-n denote magnetic tapes (media) provided in the library apparatuses 52-0 and 52-1.
In the hierarchical storage system, upon receipt of a request for data and so on, one of the hard disks 510 of the disk array apparatus 51 is to access the data. However, when there is no data in the disk array apparatus 51, the data is read in from a library apparatus 52 and written to a hard disk 510 of the disk array apparatus 51. The requested data is also read from the hard disk 510.
When the disk array apparatus 51 accesses the library apparatus 52, a medium that can perform a process earlier is selected from the duplexed library apparatuses 52-0 and 52-1. Practically, a medium (magnetic tape) of the library apparatus whose drive can be available earlier is selected. When the structure of the system is small, a plurality of media in one library apparatus is duplexed, and when the disk array apparatus 51 accesses the library apparatus, a medium that is available in the duplexed media is selected. The case where a library apparatus is duplexed is explained below.
As a conventional technique of the above mentioned hierarchical storage system, an automatic redundant copy mechanism performs preventive maintenance on each of the duplexed library apparatus to be accessed by a disk array apparatus.
FIG. 6 is an explanatory view of the automatic redundant copy. In FIG. 6, reference numerals 52-0 and 52-1 correspond to the identical reference numerals shown in FIG. 5, and reference numerals 520-1 and 521-1 denote duplexed tape media provided for the library apparatuses 52-0 and 52-1, respectively, and the same contents are stored in the tape medium 520-1 and 521-1. Reference numerals 521-2 to 521-n denote free media in the library apparatus 52-1.
The automatic redundant copy mechanism (also referred to as a tape redundant copy mechanism corresponding to a magnetic tape) copies data to another tape medium before a recording medium (tape medium) becomes faulty, and is the function of renewing a tape medium.
The outline of the process of the automatic redundant copy is described below.
#1: The statistical information (mount frequency, write frequency, read frequency, total processing time and so on for each tape medium) of a tape medium is recorded and held in the hierarchical control apparatus 50 shown in FIG. 5, and the hierarchical control apparatus checks whether or not the statistical information exceeds a threshold prescribed by a predetermined frequency or processing time. When the statistical information exceeds the threshold, the hierarchical control apparatus determines that it is necessary to replace a tape medium (perform a preventive maintenance). In the example shown in FIG. 6, it is assumed that the tape medium 521-1 in the library apparatus 52-1 has reached a replacement time.
#2: When the replacement time is reached, one of the free media in the same library apparatus is acquired. In the example shown in FIG. 6, a free tape medium in the library apparatus 52-1 is selected, and it is assumed that a new tape medium 521-m (m<n) has been acquired.
#3: All file data in the original tape medium (old medium) is copied to the acquired medium (new medium). In the example shown in FIG. 6, all file data recorded on the tape medium 521-1 as an old medium is copied to the acquired tape medium 521-m . The data can also be copied from the tape medium 520-1 of the other library apparatus 52-0 in the duplexed apparatuses.
#4: When all data are completely copied, the acquired tape medium is registered as a tape medium to be used (in a status of being assigned). In the example shown in FIG. 6, the tape medium 521-m to which data is copied is set as a new duplexed tape medium for the tape medium 520-1 in the library apparatus 52-1.
#5: The originally used tape medium is managed as a medium in a faulty state (faulty medium). In the example shown in FIG. 6, the old tape medium 521-1 of the library apparatus 52-1 is managed as a faulty medium.
A conventional duplexed control apparatus of the information record regeneration apparatus for shortening the medium replacement time for a duplexed recording medium reads data with redundancy using two media on which a mirroring process (copying data to a new medium when the data is updated in an old medium) is performed. The duplexed control apparatus saves the data temporarily when a medium is replaced, and terminates the replacement when a medium of an active system is replaced. Then, the duplexed control apparatus replaces a medium in the standby system and performs a high-speed positioning to a tape position in the active system, and regains the redundancy automatically, thereby duplexing a magnetic tape and holding redundancy without performing a complicated process by an upper apparatus and an operator and so on, and without reduction in performance when a medium is replaced (refer to Patent Document 1: Japanese Patent Laid-Open No. 2004-86251).
When a duplexed library apparatus in a hierarchical storage system is accessed, one available apparatus is accessed. Therefore, there is not a large difference in use frequency (or total processing time) between the duplexed apparatuses, and a well-balanced value is obtained. As a result, when the automatic redundant copy mechanism is started according to a statistical information of a media, there is the possibility that the two duplexed media storing the same information can be replaced for preventive maintenance at the same time.
In the technique of the above described Patent Document 1, when a medium of the active system is replaced, the medium of the standby system is simultaneously replaced. Therefore, it is different from the system such as an automatic redundant copy mechanism and so on for replacing only one of the duplexed media when the time of preventive maintenance comes.
Since the automatic redundant copy mechanism is started according to the statistical information, there is the possibility that both of the two duplexed media are evenly used, thereby allowing with high probability the automatic redundant copy mechanism to simultaneously perform preventive maintenance on the two duplexed media. In this case, there is the strong possibility of a user data lost (loss of data) due to a fault of a medium during simultaneous preventive maintenance on the two duplexed media.